Jupiter has in total 63 moons. It seems more are
discovered on a yearly basis. The
Institute for Astronomy in Hawaii has discovered
23 additional moons in 2003.
More information can be found on the Jovian Satellite Fact Sheet. There is also the The Jupiter Satellite Page - An up to date resource on Jupiter's moons as well as the other planets.
The reason for this
is pretty simply: the gravity influence of Jupiter
is pretty intense, and perturbations of the
belt is a result. Small
asteroid bodies are often
captured by Jupiter and forces to orbit. The result
is a moon of Jupiter. In fact, most of Jupiter's
asteroids. While the
four main moons
have been discussed, there are a few other important
Each of these moons orbit inside
Io - meaning
they are very close to Jupiter. These moons are
important because they are the "ring moons." They
help the rings of Jupiter keep their form and sweep
away any debris. The term for this function is
called shepherd moons. Amalthea is closest to
Io and is covered by the sulfur dust expelled by the
There are two main categories of moons: prograde
Prograde satellites rotate in the "correct" orbit
and the retrograde satellites imply capture. The
idea of this is that the prograde satellites
probably formed with Jupiter and the retrograde
satellites were captured later.
For more Jovian
moon information a
Jovian Satellite Fact Sheet is available.